As mixed materials, fiber-reinforced composite materials generally consist of at least two components. In addition to a resin component, such as for instance an epoxide, cyanate or phenolic resin, the fiber-reinforced composite materials encompass a fiber component which can consist for example of unidirectional fibers but also of nonwoven fabrics, woven fibers or chopped fibers. In combination with the resin component that is used, the fiber component that is used imparts high strength to the material, for which reason fiber-reinforced composite materials are used as composite materials in application areas with stringent requirements in terms of structural material properties, such as in aircraft construction, automotive construction or in the production of rotor blades for wind turbines.
Epoxide resins or mixtures of various epoxide resins are used as the resin component for many of these applications.
While epoxide-based fiber-reinforced composite materials have a comparatively high modulus and a comparatively high glass transition temperature, they are, however, usually brittle.
Therefore a number of proposals exist in the prior art for improving the mechanical properties of epoxide-based fiber-reinforced composite materials, in particular in the interlaminar regions of the materials. For example, rubbers, thermoplastics or certain fillers are added, often in combination, to improve toughness.
Thus, for example, a method was proposed in WO-A1-2010/108846 to allow for epoxide curing in the presence of thermoplastic particles.
To date, however, the measures proposed in the prior art have not yet been able completely to satisfy all requirements.
In addition to the completely cured epoxide-based fiber composite materials, such as are obtained with vacuum infusion and vacuum injection techniques, prepreg systems also frequently find application in industry. Epoxide-based prepregs consist of fibers which are impregnated with an epoxide resin matrix that is not yet or is only partially cured. Curing of such systems takes place at temperatures above 100° C., only after processing of the prepregs. Such epoxide-based prepreg systems offer satisfactory mechanical properties but have the disadvantage that the curing mechanism is initiated at the fiber coating stage. To avoid a premature complete cure, such fiber composite materials thus have to be stored in very cool conditions (preferably at −20° C.). If the cooling chain for such prepregs is interrupted, they cure and become unusable.